hw_timer_t *My_timer = NULL;
volatile int counter = 0;

void IRAM_ATTR onTimer400(){
    unsigned int mill = millis();
    Serial.print("Pada detik (400ms) ke : ");
    Serial.print(mill); 
    Serial.print(" , Counter: ");
    Serial.print(counter);
    Serial.print("\n");
    counter = counter+1;
}

void IRAM_ATTR onTimer600()


void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  My_timer = timerBegin(0, 16, true);
  timerAttachInterrupt(My_timer, &onTimer400, true);
  timerAlarmWrite(My_timer, 1000000, true);
  timerAlarmEnable(My_timer);
}

void loop() {
  // put your main code here, to run repeatedly:

}